Test: Structural Isomerism - 1 - NEET MCQ

C₅ H₁₀

 Two times double bond can’t appear as it has asked alkene and not alkadiene. So, these are the only types of alkenes that can be formed which are structural isomers.

n-pentane, 2-ethylpropane, and 2-methylbutane are the 3 isomeric alkanes of C₅H₁₂ (pentane).

The compounds with each doubly bonded carbon attached to two different groups (like Cab=Cab, Cab=Ccd) exhibit geometrical isomerism i.e., cis and trans forms. The geometrical isomerism arises due to restricted rotation of double bond.

However, even though there is restricted rotation for triple bond, alkynes do not exhibit geometrical isomerism, since the triply bonded carbons are attached to one group each only.

Correct Answer :- D

Explanation :

Double bond equivalent of the given compound C₄H₈O₂ is 1. So we will have compounds that have either a double bond or a ring. In option c, we have dialdehyde which is a 2 double bond compound. So it is not possible.

The formula that these isomers contain no rings or double bonds. The isomers must be alcohols and ethers.
For The alcohols
1. CH₃CH₂CH₂CH₂OH, butan 1-ol
2. CH3CH₂CH(OH)CH₃, butan-2-ol
3. (CH₃)₂CHCH₂OH, 2-methylpropan-1-ol 
4. (CH₃)₃COH, 2-methylpropan-2-ol.
Now for the ethers.
5. CH₃CH2CH₂OCH₃, 1-methoxypropane
6. CH₃CH2OCH₂CH₃ , ethoxyethane
7. (CH₃)₂CHOCH₃ , 2-methoxypropane.

General formula of ketone = C_nH_2nO
12x+2x+16 = 100
x = 6
So, the formula of compound is C₆H₁₂O. We have to make ketone only. These are as follow

Vapor density = Molecular weight/2

As both the compounds have same molecular weights, both will have the same vapour density. Hence, gaseous density of both ethanol and dimethyl ether would be same under identical conditions of temperature and pressure. The rest of these three properties; Vapour pressure, boiling point and heat of vaporization will differ as ethanol has hydrogen bonding whereas ether does not.

Tert butyl chloride will have mass in decimals (since Cl is its constituent and it has fractional mass), so it will not be considered. In Iso hexane there are 5 different positions, so we can’t get one single monosubstituted alkyl halide.
In neo-hexane, we have 3 different positions for mono substitution, so we can’t get one single monosubstituted alkyl halide.
However in neopentane, we have a single position for substitution. So we can get one single monosubstituted alkyl halide.

 In ethers, alcohols and amines, there is no double bond. However, esters have one double bond as same as monocarboxylic acid. So monocarboxylic  acid is a functional isomer of ester (only for no. of carbon greater than 2. As we need to have at least 3 carbon atoms to form ester.)

THE STRUCTURE OF ALLENE IS AS FOLLOW;
CH₂=C=CH₂
We see that there are 2 sp² hybridised carbon atoms at the extreme of the chain. While the middle carbon atom  is sp hybridised.

To determine which of the statements are correct, let's analyze each statement one by one.

Step 1: Analyze Statement I
Statement I: A pair of positional isomers differs in the position of the same functional group.

- Explanation: Positional isomers are compounds that have the same molecular formula and the same functional group but differ in the position of that functional group within the molecule. For example, consider butanol:
- 1-butanol (C₄H₁₀O) has the hydroxyl (-OH) group on the first carbon.
- 2-butanol (C₄H₁₀O) has the hydroxyl (-OH) group on the second carbon.

Thus, this statement is correct.

Step 2: Analyze Statement II
Statement II: A pair of structural isomers have the same relative molar mass.

- Explanation: Structural isomers have the same molecular formula but differ in the connectivity of their atoms. Since they have the same number and types of atoms, their molar masses will be the same. For example, both butanol and isobutanol (C₄H₁₀O) have the same molar mass despite differing structures.

Thus, this statement is correct.

Step 3: Analyze Statement III
Statement III: A pair of functional group isomers belongs to different homologous series.

- Explanation: Functional group isomers are compounds that have the same molecular formula but different functional groups. For example, ethanol (C₂H₆O) and dimethyl ether (C₂H₆O) are functional group isomers. They belong to different functional groups but can belong to the same homologous series if they have similar structural features. Therefore, this statement is incorrect.

Methyl methanoate and ethanoic acid are functional group isomers as they have the same molecular formula but the connectivity differs.
Since they have different functional groups, they belong to different homologous series.
Different homologous series have different properties.

They are positional isomers, hence same molecular formula C₅H₈Br₂. However, they are structure isomers, hence different physical and chemical properties.

C₄H₈ structural isomers are as follow:-

so 5 isomers are possible

Double bond equivalent of C₅H₁₀O is 1. So, it will have either a double bond or a ring.So, it may be an aldehyde, ketone, alcohol( carbon chain having double bond) or epoxide.
Propyl ethanoate has 2 oxygen atoms. So, it will never be its isomer. HOwever option a and c will be its isomer as they are aldehyde.

The reason behind this is that only for no. of carbon atoms greater or equal to 4, we can make different chains or rings. So, the answer is a